As for technology for automatically measuring a shape or a position of an object, various methods based on a three-dimensional shape measuring method are known.
As one method, there is a light sectioning method of capturing an image of a target object with a camera while irradiating and moving a linear laser beam with use of a galvano-mirror and measuring a detailed three-dimensional shape of the target object based on linear reflection position (curve) of the captured image. The advantage of this method is that the shape of the object can be measured with extremely high precision.
As a second method, there is a method of capturing an image of a target object with a camera by uniformly irradiating light to the target object, utilizing properties in which near areas look bright and far areas look dark in the image, and measuring the depth of each position in the image.
As a third method, there is a method which does not rely on the three-dimensional shape measuring method. In the third method, plural markers are attached to a target object and the locations of the markers are measured.
With the above-described first-third methods, a position of an object can be obtained by, for example, measuring the shapes or the like of a target object, detecting locations of joints based on measured data of the shapes, and calculating the angles of the joints.
The above-described first-third methods have the following problems.
The first method has problems such as requiring a specialized apparatus such as a laser irradiation mechanism, taking up large space, requiring large cost, and requiring time for scanning. Thus, the method is applicable to only limited special purposes.
The second method has problems such as presuming that the materials or patterns on the surface of a target object do not change regardless of whether the target object is a solid and therefore being unable to perform accurate measurement where there is individual difference and/or a change of physical property of the surface of the target object.
The third method has problems such as requiring a laborious task of attaching markers onto a target object and being unable to handle a case where markers cannot be attached in the first place.
Further, Japanese Laid-Open Patent Publication No. 2004-328657 discloses a method of capturing a first image of a target object by irradiating strobe light to the target object, capturing a second image of the target object without irradiating light to the target object, and obtaining a difference between the two captured images, to thereby obtain information of depth of the target object. However, since the information of depth is obtained based on brightness, this method has the same problems as the second method of being unable to accurately measure, for example, reflectivity or the shape of the target object.
Further, Japanese Laid-Open Patent Publication No. 2007-174566 discloses a method of detecting eyes that become red due to flash of a camera based on a difference between a single lens image obtained before switching to flash and another single lens image obtained after switching to flash, and extracting a facial area within an image based on the locations of the detected eyes. However, since this method detects the contour of a face by a regular image processing method, the contour of a face cannot be accurately detected due to changes in the condition and/or the background of the target object and the facial area cannot be precisely extracted.